A massive police hunt was under way in Seattle and its surrounding suburbs for the habitual criminal who is the prime suspect in a brutal murder yesterday morning in which four police officers were killed in cold blood as they sat in a cafe drinking coffee.

Swat teams surrounded and bombed with tear gas a Seattle home in which the suspect, Maurice Clemmons, was thought to have been present. But after an operation that lasted several hours the house was found to have been empty.

"He has been shot and he is armed and he knows we are looking for him. We believe him to be very desperate and dangerous," said Ed Troyer, the spokesman for the sheriff's office in Pierce county where the murders happened.

Details emerged overnight about Clemmons's troubled past and history of mental disturbance. According to police reports compiled over the past few months, he has had delusions that he could fly and that he is the Messiah.

His sister told police that he was convinced the secret service was out to get him because he had written a letter to President Barack Obama. He also believed the world was coming to an end.

Earlier this month he was given a psychiatric examination which concluded he was able to stand trial on charges brought against him in the summer.

Clemmons, 37, has also had a long string of prosecutions against him dating back to when he was 17 and living in Arkansas. In 1990 he was given a 60-year jail sentence for burglary and theft of property.

In 2000 he was released after 11 years in circumstances that could prove politically awkward for Mike Huckabee, who is considered a possible Republican presidential candidate in 2012. As governor of Arkansas he granted clemency to Clemmons, even though he was advised not to do so by prosecutors.

"This is the day I've been dreading for a long time," Larry Jegley, an Arkansas prosecutor, told the Seattle Times.

As news of the Huckabee clemency spread through the internet, parallels were being drawn with Michael Dukakis, the Democratic politician whose 1988 presidential run was partially derailed by a Republican ad campaign that highlighted his support for a programme of weekend release that had allowed out a life prisoner, Willie Horton, who went on to commit rape.

In a statement put out hours after the murders, Huckabee sought to spread any blame to other parties involved in decisions about Clemmons's release.

He said that Clemmons had been allowed out by the parole board and that "he was arrested later for parole violation and taken back to prison to serve his full term, but prosecutors dropped the charges that would have held him."

Clemmons had a record of at least eight felony charges in Washington and five in Arkansas, but partly as a result of procedural wrangling and partly as a result of the ball being dropped by the authorities in the two states he frequently avoided detention or treatment for his mental health issues.

In the most recent incident, he was released from custody last Tuesday despite facing seven charges relating to an incident in May in which he punched a police officer in the face. He also faces child rape charges linked to his alleged abuse of a 12-year-old female relative.

New details emerged about how the killings unfolded. Two women workers who were serving coffee in the Forza Coffee shop in Lakewood outside Seattle yesterday said they had seen an African-American man walk into the cafe and approach the counter.

He then pulled up his coat, removed a gun and turned around to face the four police officers who were sitting working on their laptops before the start of their morning shift. He shot and killed three of the officers on the spot, and went on to have an exchange of fire with the fourth officer before he too was killed.

Detectives leading the manhunt hope that the suspect may have been wounded in the firefight, and that his injuries may lead police to him.